How to create a center pivot point for mutiple mesh files?
If you want all meshes to have the same, centred origin:


Select all meshes you want to average the centre from
Snap - Cursor to selected (or place your 3D cursor where you want their centre to be)
Snap - Origin to 3D cursor


I use the "3D View: Dynamic Context Menu" addon to easily find these

You could also join the meshes together with Ctrl+J, depends on the use case I suppose.

I guess in your case for export you might want to move their centre to the origin of the scene afterwards to have their centre be the same in the export